The overall aim of the research program in this laboratory is to provide an understanding of the cortical circuitry that underlies specific response properties of visual cortical neurons. The research proposal outlined here is specifically directed toward analyzing widespread, patchy, intrinsic connections that arise in the geniculate (LGN) recipient layers 5 and 6 and terminate in the principal LGN input layers, 4 and 2/3, of rat primary visual cortex. Initial experiments will characterize the type(s) of neurons that contribute to these connections. Specifically, they will determine whether each connection is made up of cells with different morphologies that express different transmitter markers and have different physiological properties. Subsequent experiments will examine the spatial relationship between the clustered projections from layers 5 and 6 in the terminal layers 2/3 and 4. In addition, we will investigate the relationship between these intrinsic projections and the organization of inputs from the LGN, and will evaluate anatomical diversities relating to functionally different geniculocortical pathways. These studies will be approached employing a combination of in vivo and in vitro labeling techniques, whereby specific layer 5 and 6 cells will be identified, physiologically characterized and injected intracellularly with dye in in vitro brain slices. Injected cells will be stained for GABAergic and peptidergic markers and with antibodies against excitatory amino acids. The spatial relationships of different intrinsic and extrinsic projections will be determined through in vivo and in vitro anterograde labeling of projections with fluorescent dyes. These studies will provide insight into the anatomy and physiology of intrinsic cortical connections made by non-pyramidal cells.